I actually had an idea about this. It seems to me that if you run a hose under the car and into the trunk, you could attach that hose inside the car to one of the floor vents. Have a fan on the other side that sucks the cool air down the line and into the computer case. I'll figure out how to do mine and post some instructions.
You normally don't have hot air blowing on your face, so having this on the upper vents can work. You just have to remember not to have it on heat + vent. Btw, is anyone using the newer heatpipe coolers?